A vertical thermal processing apparatus for collectively processing a plurality of semiconductor wafers (hereinafter referred to as “wafers”) is used in a semiconductor manufacturing process for forming a film. Operation of the vertical thermal processing apparatus begins by loading a substrate holder holding a plurality of substrates in a shelf shape into a vertical reaction container surrounded by a heating part from a lower opening of the reaction container, covering the opening with a lid, and supplying a processing gas into the reaction container.
In such an apparatus, a lot of particles adhere to a bottom portion inside the reaction container, especially an inner surface of the lid. The reasons for this are considered to be that many quartz members are present inside the reaction container, particles are dropped to the bottom under the force of gravity, a mechanism for opening and closing the lid is placed near the bottom portion of the reaction container, and deposits adhering to the inside of an exhaust pipe return into the reaction container.
For example, in an apparatus for cleaning the inside of a reaction container by a cleaning gas each time when a film is formed on a substrate, a heater may be provided in a lid to prevent liquefaction of the cleaning gas at the time of cleaning. However, a temperature of the lid and its vicinity is much lower than a processing temperature in a processing atmosphere. Therefore, when the substrate is subjected to a film forming process such as, for example, CVD (Chemical Vapor Deposition) or the like, a film does not adhere to the bottom portion inside the reaction container.
As such, the particles (foreign substances) adhering to the bottom portion inside the reaction container are free to move. When the lid is opened, the particles are moved upward by an airflow generated due to a slight pressure difference between the inside and the outside of the reaction container. This may cause wafer contamination. In the past, the inner surface of the lid was manually cleaned regularly. This increases the burden for workers, which results in a reduction in the operation efficiency of the apparatus.
For example, a technique has been used for forming a polysilicon film as a pre-coating film inside a reaction container at 600 degrees C., prior to performing an epitaxial growth on a wafer using a vertical thermal processing apparatus. However, the pre-coating film is used for protecting a quartz member from a hydrogen fluoride gas for removal of a natural oxide film and is not formed on the bottom portion of the reaction container kept at a low temperature. Therefore, the aforementioned technique is not a technique that suggests the present disclosure.